1. Field of the Invention
This invention relates to a roller device, more particularly to a roller device for a toner cartridge of a laser printer.
2. Description of the Related Art
Referring to FIG. 1, a toner cartridge 1 of a currently existing laser printer includes a casing 11, a photo conductor drum 12 disposed in the casing 11, a developer roller 13 and a primary charge roller 14 abutting against a periphery of the photo conductor drum 12 and angularly spaced apart from each other, and a transfer roller 15 abutting against the periphery of the photo conductor drum 12 and located between the developer roller 13 and the primary charge roller 14.
In use, the primary charge roller 14 guides uniformly a negative electrostatic charge to the periphery of the photo conductor drum 12, after which the developer roller 13 spreads the toner to the periphery of the photo conductor drum 12 at required locations. Finally, the photo conductor drum 12 is pressed over a paper 100 to transfer the toner to the paper 100 through the transfer roller 15, thereby completing a printing job.
Referring to FIG. 2, in combination with FIG. 1, each of the rollers 13, 14, 15 of the toner cartridge 1 includes a roller body 21, and a metal rod 22 inserted into the roller body 21. The roller body 21 includes a tubular sleeve 211 made of polyamide, and a foam body 212 filled within the tubular sleeve 211 and made of polyurethane. The metal rod 22 is inserted into the foam body 212.
Due to the fact that a connecting force between two different materials is poor, the tubular sleeve 211 and the foam body 212 cannot completely and tightly adhere to each other. Thus, the problem of poor printing quality always exists. In order to enhance the connecting force between the tubular sleeve 211 and the foam body 212, an inner wall of the tubular sleeve 211 is applied with an adhesive. However, this only complicates the manufacturing process of the aforementioned rollers 13, 14, 15. The conventional manufacturing process involves forming the foam body 212 on an outer periphery of the metal rod 22 first, after which the tubular sleeve 211 is sleeved on an outer periphery of the foam body 212. Alternatively, the metal rod 22 may be inserted first into the tubular sleeve 211 and positioned therein, after which the foam body 212 is filled within the tubular sleeve 211, thereby obtaining the aforementioned structure of the rollers 13, 14, 15. However, to position the metal rod 22 in the soft-quality tubular sleeve 211 is difficult. Even after the metal rod 22 is positioned in the tubular sleeve 211, when the foam body 212 is filled within the tubular sleeve 211, the metal rod 22 easily displaces. Hence, the rollers 13, 14, 15 are deflected during rotation of the same. This results in printing defects.
Moreover, although the foam body 212, which is made of polyurethane, decomposes naturally, when connected with the tubular sleeve 211, which is made of polyamide, using an adhesive as described above, the assembly of the foam body 212 and the tubular sleeve 211 is not easily recycled for reuse.
To resolve the aforementioned problems associated with a complicated manufacturing process and poor connection between different materials, U.S. Pat. No. 6,945,921 discloses a roller that is coated with a polysiloxane containing carbon black resin layer to ensure a tight connection between layers of materials. However, the coating process is time-consuming. Also, it is difficult to thicken the coating layer, so that the polysiloxane containing carbon black resin layer is thin, and is thus easily worn off, thereby affecting the service life of the toner cartridge.